The mechanisms of negative type are known to ensure positive control of the heddle frames only in one direction of displacement, with the result that elastic elements must be provided to return the frames in the other direction of a stroke.
In fact, and as has been schematically shown in FIG. 1 of the accompanying drawings, the elastic elements associated with each heddle frame are most often constituted by two series or "registers" 1 of parallel springs 1a. In each register 1, the springs 1a are retained between a rack 2 fixed to the vertical structure 3 of the weaving machine and a clip element 4 which is suspended from an oscillating lever 5. The lever 5 is mounted to a horizontal shaft or pivot 6 carried by the structure 3. On each of the two oscillating levers 5 associated with each heddle frame 7 there is connected one end of a transmission element, most often formed by a cable 8 which is secured to the frame 7 to be controlled and of which the free end, suitably guided, is hooked to the moveable member for actuating the weaving mechanism.
It will be understood that such a drawing system ensures control of the heddle frame 7 since the displacement of the moveable member provokes lowering of the frame to its lowest position against the registers 1 which are adapted to return the assembly to the upper position by action on each lever 5 as soon as the moveable member of the mechanism returns to its initial position.
The increase in the operational speeds now required of weaving machines requires an increased number of springs 1a in each register 1. To limit the efforts to be furnished by the weaving mechanism, the number and type of springs should be modified as a function of the speed of weaving and the nature of the article to be woven. Furthermore, it is not rare for a spring to break in one of the registers, so that interventions are relatively frequent.
Now, it has been shown in practice that replacement of springs is difficult due to the large number of springs in each register, the high force of these springs and the very location of the registers in the weaving machine.